Various methods have been developed for growing crystalline bodies from a melt. One such method is known as the EFG ("Edge-defined, Film-fed Growth") process. Details of the EFG process and of apparatus for growing crystalline bodies according to the EFG process are described and illustrated in U.S. Pat. No. 3,591,348 issued Jul. 6, 1971 to Harold E. La Belle, Jr. for "Method of Growing Crystalline Materials", and in U.S. Pat. No. 3,687,633 issued aug. 29, 1972 to Harold E. La Belle, Jr. et al. for "Apparatus for Growing Crystalline Bodies from the Melt".
In the EFG process, a capillary-forming die member is placed in association with a melt of liquid source material so that a growth face on the die member is wetted with a liquid film of source material from the melt by capillary action. A product crystalline body is then grown by first introducing a seed crystal to the liquid film of source material so that crystal formation is initiated, and then drawing the seed crystal away from the growth face at a controlled rate so that the liquid film of source material remains sandwiched between the growing crystalline body and the growth face of the die member. Since the liquid film of source material on the die's growth face is continuously replenished from the melt by the die's one or more capillaries, continuous crystalline bodies of significant size may be grown from the melt.
One consequence of the EFG process described above is that the cross-sectional shape of the product crystalline body is determined by the shape of the growth face of the die member. As a result, by appropriately shaping the growth face of the die member, crystalline bodies may be grown which have the shape of a round rod (i.e., where the crystalline body has a cross-sectional shape which is that of a solid circle), a flat ribbon (i.e., where the crystalline body has a cross-sectional shape which is that of a solid rectangle), a hollow tube (i.e., where the crystalline body has an annular cross-section of circular, elliptical or polygonal shape), etc.
The present invention is directed to apparatus adapted to grow tubular crystalline bodies according to the EFG process.
Existing apparatus for growing tubular crystalline bodies according to the EFG process is described and illustrated in U.S. Pat. No. 4,230,674 issued Oct. 8, 1980 to Aaron S. Taylor et al. for "Crucible-Die Assemblies For Growing Crystalline Bodies Of Selected Shapes", U.S. Pat. No. 4,440,728 issued Apr. 3, 1984 to Richard W. Stormont et al. for "Apparatus For Growing Tubular Crystalline Bodies", and U.S. Pat. No. 4,544,528 issued Oct. 1, 1985 to Richard W. Stormont et al. for "Apparatus For Growing Tubular Crystalline Bodies".
In practice, it has been found that significant improvements in crystal quality can be obtained if one can control the atmosphere surrounding the growing crystalline body. This is because control of the atmosphere surrounding the growing crystalline body allows harmful reactive gases to be removed from the area surrounding the growing crystalline body while allowing inert gases, beneficial reactive gases, and/or beneficial doping gases to be introduced to the area surrounding the growing crystalline body. In addition, control of the temperature of the atmosphere surrounding the growing crystalline body can facilitate proper regulation of the temperature of the growing crystalline body.
U.S. Pat. No. 4,415,401 issued Nov. 15, 1983 to Fritz Wald et al. for "Control Of Atmosphere Surrounding Crystal Growth Zone", U.S. Pat. No. 4,443,411 issued Apr. 17, 1984 to Juris P. Kalejs for "Apparatus For Controlling The Atmosphere Surrounding A Crystal Growth Zone", and the publication "Modeling Of Ambient-Meniscus Melt Interactions Associated With Carbon And Oxygen Transport In EFG Of Silicon Ribbon" by J. P. Kalejs and L. Y. Chin, published in the Journal Of The Electrochemical Society, Vol. 129, No. 6, June 1982, teach ways of controlling the atmosphere surrounding a growing crystalline body where that body is a flat ribbon. Unfortunately, these references are silent as to how to control the atmosphere surrounding the growing crystalline body where that body is in the form of a hollow tube. In this respect, it is noted that the problems of controlling the atmosphere surrounding the growing crystalline body are magnified significantly in the case of apparatus adapted to grow hollow tubes, since in such apparatus the body of the growing hollow tube serves to effectively divide the atmosphere surrounding the growing crystalline body into an "exterior" zone (i.e., the zone located outside the growing crystalline body) and an "interior" zone (i.e., the zone located inside the growing crystalline body), because the walls of the growing crystalline body serve to prohibit the direct flow of gases between the "exterior" and "interior" zones and gases can only flow between the two zones by passing through the seed holder located at the remote end of the hollow crystalline body.